1. Field of the Invention
The present invention provides a method of fabricating a thin-film-transistor liquid-crystal-display (TFT-LCD), more particularly, a method of making the TFT-LCD by a five-masks process with redundant interconnections.
2. Background of the Invention
Due to the continued development and advancement in electrical technology, the range of application of a flat panel display is also increased. The kinds of the present flat panel display include liquid crystal displays (LCD), plasma display panels (PDP), electro-luminescent displays (ELD), field-emission displays (FED) light emitting diode displays (LED), and vacuum fluorescent displays (VFD).
A TFT-LCD usually includes a plurality of thin film transistors with a matrix structure, capacitors, and connecting pads to drive a plurality of liquid crystal pixels so as to generate color-rich graphics. A conventional LCD includes a transparent substrate having a matrix of thin film transistors, pixel electrodes, scan lines, signal lines, a color filter substrate, and a layer of liquid crystal materials positioned between the transparent substrate and the color filter substrate. Since the TFT-LCD is the advantages of lightweight, low energy consumption, and radiation free, it is employed in various portable electronic devices such as a notebook and PDA. Further, the TFT-LCD is slowly replacing the CRT of desktop computers.
Please refer to FIG. 1. FIG. 1 is a layout diagram of the conventional thin film transistor liquid crystal display (TFT-LCD) 10. The conventional TFT-LCD 10 is manufactured on a transparent glass substrate 11. As shown, on the glass substrate 11 are at least a thin film transistor(TFT) 40, a plurality of scan lines 12, and a plurality of signal lines 14 which are perpendicular to the scan lines 12. In the TFT-LCD 10, each thin film transistor 40 includes a gate electrode 42, a source 43, and a drain 44. Each TFT is used to drive a corresponding pixel electrode 16, which is made of indium tin oxide (ITO) layer, on the substrate 11. The gate electrode 42, usually made of polysilicon, is formed with the scan lines 12 at the same time. The source 42 and the drain 44 respectively connect with the pixel electrode 16 and the signal lines 14 via contact holes 46 and 48. For simplicity, other components of the TFT-LCD 10, such as the capacitor and connecting pad are omitted in FIG. 1.
According to the prior art, a redundant transparent conductive line 30 is formed to prevent short circuit of the signal lines 14. The redundant transparent conductive line 30 is formed above the signal line 14 and simultaneously formed with the pixel electrode 16. The transparent conductive line 30 is an ITO layer, and connects with the source electrode 43, drain electrode 44, and the signal line 14 through a source contact hole 46, a drain contact hole 48 and a signal line contact hole 52, respectively.
Usually, the signal lines 14 and the scan lines 12 are formed on different surfaces, this is to say, at least one layer is formed between the signal line 14 and the scan line 12, such as a semiconductor layer or an insulating layer. Hence, a short circuit may occur at the crossing region 32 of the signal lines 14 and scan lines 12 because the uneven surface of the intersection 32. To solve the problem, the ITO line 30 is formed over the signal line 14 to be a redundant line in the conventional method. The redundant line 30 can establish a connection with the signal line 14 via the signal line contact hole 52, so as to transmit the signal even a short circuit of the signal line 14 is happened at the crossing region 32.
However, the redundant ITO line 30 may be connected to the pixel electrode 16 because of the contaminants produced in the manufacturing process, resulting in a short circuit or a point defect, and the yield of the TFT-LCD 10 is reduced. In FIG. 1, the defect region marked by a dotted frame 50 represents the most likely region of the point defects. Thus, reducing the point defect is important in improving the yield of the TFT-LCD 10.
It is therefore a primary object of the present invention to provide a method of fabricating a thin film transistor liquid crystal display (TFT-LCD) to minimize the defect region, so as to increase the yield of the TFT-LCD.